**Abstract**

Type 2 Diabetes Mellitus is associated with both macro- and microvascular complications. One among the latter, is cardiovascular autonomic neuropathy (CAN). CAN is attributed to cardiac arrhythmias and sudden death. Underlying pathogenesis of cardiac autonomic neuropathy is chronic hyperglycemia induced oxidative stress causing neuronal necrosis, apoptosis and death, leading to the sympathetic and parasympathetic nerve dysfunction. The balance between sympathetic and parasympathetic nervous system is reflected by heart rate variability (HRV). HRV describes "the variations of both instantaneous heart rate and R-R intervals which in turn reflects the cardiac autonomic nervous control". HRV measured at rest is a marker of autonomic nerve function status. Thus, HRV test is recommended to diagnose diabetic CAN. Time domain parameters predominantly reflect overall autonomic activity and parasympathetic nervous system (PNS) modulations. Frequency domain parameters either reflect, sympathetic nervous system (SNS) activity, PNS activity, or the balance between the two activities. Nonlinear HRV indices marks PNS influences, SNS influences and sympatho-vagal balance. Almost all these HRV parameters are remarkably reduced in T2DM due to cardiac autonomic dysfunction. HRV is an important simple and noninvasive diagnostic tool to detect CAN.

**Keywords:** type 2 diabetes mellitus, oxidative stress, heart rate variability, cardiac autonomic neuropathy, time domain, frequency domain
